Radio communication systems that can transmit high bit-rates are currently experiencing strong growth. The systems being developed, particularly the point-to-multipoint systems such as the LMDS (Local Multipoint Distribution System) systems and WLAN (Wireless Local Area Network) wireless systems, operate at increasingly higher frequencies, namely in the order of several tens of Giga-Hertz. These systems are complex but must be realized at increasingly lower costs due to their use by consumers. There are now technologies such as LTCC (Low Temperature Cofired Ceramic) or HTCC (High Temperature Cofired Ceramic) technologies that enable devices integrating passive and active functions operating at the above frequencies to be realized at low cost on a planar substrate.
However, some functions are difficult to realize in the millimetric band, particularly filtering functions, because the substrates that must be used in this case do not have the qualities required at the millimeter-waveband level. This type of function must therefore be realized by using conventional structures such as waveguides. Problems then arise with the interconnection of the waveguide device and the printed circuit realized using microstrip technology designed for use by the other functions of the system.
On the other hand, for identical reasons depending on their operation in millimeter wave frequencies, the antennas and their associated elements, such as filters, polarizers or orthomode transducers, are also realized using waveguide technology. It is therefore necessary to be able to connect the circuits realized using waveguide technology to the planar structures realized using conventional printed circuit technology, this latest technology being suitably adapted for mass-production.
Consequently, many studies have been conducted on the interconnection between a waveguide structure and a planar structure in microstrip technology. Hence, the article of the 33rd European Microwave Conference at Munich, in 2003, page 1255, entitled “Surface mountable metallized plastic waveguide filter suitable for high volume production” of Muller et al, EADS, describes a waveguide filter capable of being connected to multilayer PCB (Printed Circuit Board) circuits by using the SMD (Surface Mounted Device) technique. In this case, the input and output of the waveguide filter are soldered directly onto footprints realized on the printed circuit. These footprints supply a direct connection to a microstrip line. Hence, the excitation of the waveguide mode is carried out by direct contact between the microstrip access lines and the guide structure. This transition therefore proves complicated to realize and requires stringent manufacturing and positioning tolerances.
A transition between a rectangular waveguide and a microstrip line has also been proposed in French patent 03 00045 filed on Jan. 3, 2003 in the name of THOMSON Licensing S. A. This transition requires modelling the extremity of the waveguide in a particular manner and realizing the microstrip line on a foam substrate extending the foam structure in which the ribbed waveguide is realized. In this case the foam bar forming the waveguide is also used as a substrate for the microstrip line. This type of substrate is not always compatible with the realization of passive or active circuits.